When the oleum sulfonation process is used for the sulfonation of detergent alkylates, a substituted organic sulfonic acid is produced, together with large amounts of unreacted sulfuric acid which remain in the first stage reaction mixture. Since sodium sulfate is a commonly used inorganic filler in spray dried detergents, it would be desirable to neutralize such reaction mixture to produce a mixture of sodium alkylate sulfonate and sodium sulfate for use in the producing the spray dried detergents. However, neutralization of the mixed acids as they come from the first stage of the oleum sulfonation process involves difficult problems. If sodium hydroxide solution is used, the intensely exothermic reaction with the sulfuric acid causes thermal decomposition of the labile organic sulfonate in the presence of unreacted sulfuric acid and results in an unacceptably dark product. If alkali carbonate solutions are used for the neutralization, there is generation of copious amounts of carbon dioxide gas, producing unmanageable quantities of foam. Problems such as these are referred to in U.S. Pat. No. 2,594,875 to Condit and 3,425,948, to Otrbalek et al. and in U.K. Pat. No. 1,369,269.
In view of the above, the current procedure for oleum sulfonation and subsequent neutralization consists of a milder process which is conducted in three stages, as follows: In the first stage, oleum sulfonation is carried out to produce the mixed organic sulfonic acid and large quantities of unreacted sulfuric acid, as referred to above. In the second stage, water is added and, after removal of the heat of dilution, the mixture separates by gravity into a lighter organic sulfonic acid layer containing about 5 to 10% sulfuric acid and a heavy phase of about 80% sulfuric acid, commonly referred to as "spent acid". The spent acid is discarded. In the third stage, the organic sulfonic acid/sulfuric acid phase is reacted with dilute sodium hydroxide to form a slurry of from 40 to 60% sodium alkylate sulfonate, with 5 to 10% of sodium sulfate. The resulting slurry is commonly mixed with inorganic builder salts, inorganic fillers, antiredeposition agents, fluorescent whitening agents, sodium silicates, etc. to form a slurry which is then spray dried to a granular laundry detergent.
In the above current procedure, the elimination of the spent acid, together with the use of diluted sodium hydroxide, produces a milder, more readily manageable reaction. However, the discarding of the spent acid not only constitutes a waste of materials, but it has become a disposal problem since it is considered hazardous. Further, the use of water in the second stage and the water-dilution of the sodium hydroxide in the third stage introduce excess water which is costly to remove when the resulting slurry is subsequently spray dried.
Numerous U.S. patents have dealt with the problem of neutralizing various sulfonic acids with alkaline carbonates or other agents. Examples of such patents are r U.S. Pat. Nos. 2,594,690 to Shiffler; 2,975,141 to Blinoff et al; 2,982,736 to Dvorkovitz et al; 3,180,699 to Ballestra; 3,472,784 to Poe; 3,726,813 to Borrello; 3,772,204 to Insignares and 3,867,316 to Frank et al. However, none of the prior art patents provide a process of utilizing the mixed acids as they come from the first stage of the oleum sulfonation process, to produce a high solids, pumpable slurry suitable for subsequent spray drying.
It is an object of the present invention to provide such a process, in which the first stage mixture of organic and inorganic acids from the oleum sulfonation process are directly neutralized to produce a high solids slurry suitable for use in the production of spray dried laundry detergents.
It is another object of the invention to enhance oleum sulfonation plant capacity by eliminating certain exothermic stages from the process.
It is a further object to produce useful detergent ingredients from the spent acids which are currently discarded, while at the same time eliminating the substantial hazardous waste costs involved in disposing of the spent acids.
A further object is to reduce the amount of water added to the spray drying process stream.
A still further object is to provide for the use of a less costly neutralizing agent.
Other objects and advantages will be apparent from the following description and examples